Definition of an "engine-driven electrical system"?

Discussion in 'Instruments / Avionics / Electrical System' started by cluttonfred, Apr 9, 2019.

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  1. Apr 9, 2019 #1

    cluttonfred

    cluttonfred

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    Quick question...does anyone know if an "engine-driven electrical system" is defined anywhere by the FAA? I ask because I know that many two-stroke engines have a "lighting coil" that does provide enough power for some anti-collision lights and a few instruments but I don't think they are required to have a transponder. I am also wondering about a closed circuit system with an alternator or generator and battery used only for ignition and possibly electric start but independent from a battery-powered system used for the radio. Cheers, Matthew
     
  2. Apr 9, 2019 #2

    Dana

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    I believe that the typical 2-stroke engine's lighting coil has been defined to not be an engine driven electrical system. Trying that approach with an alternator and battery would be a real stretch, though.
     
  3. Apr 9, 2019 #3

    TFF

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    If you have a gen or alt hooked to the engine for charging a battery, you have an electrical system. If you just have a battery, you don’t. Wind drive is not hooked to the engine but also does not have much charging capacity. I like total loss on non travel planes. Get to have a starter but get to dump adsb I’m putting a starter on my plane, but leaving the battery on the ground. Plug in, start, cast off plug. It’s a 30 min flight plane not a traveling machine.
     
  4. Apr 9, 2019 #4

    12notes

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    Aircraft Spruce sells a 12V 4A wind generator. It won't recharge a battery quickly from a start, but it's more than enough to keep LED nav lights & radios running in the air without draining the battery, so it should work for a travel plane. I'm not sure what the current draw of coils or a fuel injection system is, I don't know if it would be enough for that.

    A wind generator with more capacity would be fairly easy to build, at the cost of more drag.
     
  5. Apr 9, 2019 #5

    Wanttaja

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    I agree with Dana, in that the FAA announced that the "lighting coil" systems would not be considered as an "engine driven electrical system" as far as transponder installations went, but I'll be darned if I can come up with a specific reference.

    Here's a story about a guy with a successful wind generator on his Fly Baby:

    http://www.bowersflybaby.com/tech/wind2.html

    Ron Wanttaja
     
  6. Apr 9, 2019 #6

    Toobuilder

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    I have thought about using a small alternator to power an EI. Seems to me that if you could show that there was no "excess" power beyond the ignition then it should be the same as a magneto. I know it's a stretch, but it would be nice to know the reasoning for the distinction between engine driven and wind, solar or total loss.
     
  7. Apr 9, 2019 #7

    Wanttaja

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    I'd say it boils down to capacity and consistency.

    A transponder is a relatively high-power device, so the airplane has to have a moderate capacity electrical system. Wind generators typically don't produce that much power...in the link I posted above, the generator produces all of four amps. A "casual" solar installation (vs. one that builds-in arrays across the tops of the wings, etc.) probably produces less than that. A total loss system is always discharging and there's always the potential it's going to discharge low enough so that things stop working.

    The FAA stipulation of an "Engine Driven Electrical System" is actually a reasonable approach. The smallest generators on traditional engines produce at least 15 amps, which is enough for a radio, transponder, and keeping the battery charged. Not so much for lights as well, in the old days (different now with LEDs) but an engine-driven system did pretty much set the threshold for a "usable" electrical system.

    One can also dance on the head of a pin regarding interpreting the rule, in regards to homebuilt aircraft. 14CFR 91.215 says....

    "Notwithstanding paragraph (b)(2) of this section, any aircraft which was not originally certificated with an engine-driven electrical system or which has not subsequently been certified with such a system installed...may conduct operations in the airspace within 30 nautical miles of an airport listed in appendix D, section 1 of this part...."

    Does "originally certificated" refer to the Airworthiness Certificate, or the TYPE Certificate? The FAA's usual practice is to use "Certificated" to refer to aircraft with Type Certificates. But, of course, my airplane does not have one. The next phase amplifies the impression that it refers to Type Certificates... "which has not been subsequently certified with such a system..." Homebuilts do not receive new Airworthiness Certificates when they are modified. They may re-enter the Phase 1 test period, but the validity of the Airworthiness Certificate does not change.

    Not so with certified airplanes. Add an electrical system to one, and you must obtain a SUPPLEMENTAL Type Certificate (STC). Again, Type Certificate, not airworthiness.

    So I think the argument can be made that ALL homebuilts are excluded from the transponder and ADS-B requirements in the Veil airspace, on the basis them "not being certified with an engine-driven electrical system." Still required to actually enter Class B and C, of course.

    Finally, then, we get to the delicate issue of proof. What evidence do I have that my airplane had an electrical system when it received its original Airworthiness Certificate? None. There's nothing in the logbooks about it. Sure, there are mentions later when various maintenance work is logged regarding the generator, regulator, and battery. But the airplane records do not show that the bird was "subsequently certified with such a system."

    My airplane is worth about $8,000. It's irritating as hell that I have to spend between a quarter and a half the value of my airplane because some pilots can't be bothered to look for traffic outside the airplane.

    Ron Wanttaja
     
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  8. Apr 9, 2019 #8

    BJC

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    Overheard in the FAA ADS-B planning office.

    FAA1, “What are we going to do about all those little old airplanes that don’t even have transponders.”

    FAA2, “Well, if they don’t have an electrical system, we’ll exempt them.”

    FAA1, “So what is the definition of an electrical system?”

    FAA2, “Isn’t it obvious? The engine drives a generator to make electricity.”

    FAA1, “Sounds reasonable enough. Let’s go with it.”

    And so the regulation was written.


    BJC
     
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  9. Apr 9, 2019 #9

    bmcj

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    Let me add a new twist to this. Does ‘engine’ mean that which directly generates thrust for flight? If so, what if you had an engine with no generator, but carried a small internal engine (not connected to the thrust line) that was used solely to generate electricity?

    Yes, I know it is not a very realistic scenario, but it potentially could be if someone were to build an electric powered plane with an internal IC sustainer (power generator) engine.

    By the way, I don’t need an answer... I only asked this to confuse the matter more (the devil made me do it). ;)
     
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  10. Apr 9, 2019 #10

    Wanttaja

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    For that matter, an electric-powered aircraft shouldn't need a transponder, either. Not only does it have a motor, not an engine, said motor probably doesn't turn a generator.....

    Ron Wanttaja
     
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  11. Apr 9, 2019 #11

    Toobuilder

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    I'd like to think the practical reason is capacity, but I'd bet it was just an arbitrary line in the sand based on the technology of the day.

    A little SD-8 mounted on the vacuum pad would handle a dual EI, but could NOT also handle a transponder... It seems unreasonable to consider that an "electrical system". It's more in line with the lighting coil of a small two stroke.
     
  12. Apr 9, 2019 #12

    Dana

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    Naturally, I like that interpretation, but I'd hate to be the one to test it...
     
  13. Apr 9, 2019 #13

    Toobuilder

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    How about this: your alternator is the little 8 amp unit that feeds the ignition adequately, but there is no transponder available which can operate on the meager surplus amperage... Do the Feds require you to install a larger alternator just to.feed the transponder?

    Seems like a chicken/egg thing. Which "requirement" has more legal pull?
     
  14. Apr 9, 2019 #14

    pictsidhe

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    So, if you don't have a $300 generator, you can get out of retrofitting a $3k transponder?
    Gotta love whoever thinks this stuff up.
     
  15. Apr 10, 2019 #15

    Pops

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    Back when I was getting my night flying for my private rating I owned a 1947 Ercoupe with a 15 amp generator and 35 amp battery. Based at a large airport. Not enough power to operate position lights, landing lights, RB , tube radio. After landing and trying to taxi to the ramp there wasn't enough in the battery to operate the radio or have any lights unless I stopped and get the engine above 1200 rpm for the generator come on line so the tower could see a light so they knew were I was at trying to taxi to the ramp, ( also about all the brakes would hold). Go a short distance and stop and rev the engine and then another distance. Now I know why it had a 35 amp battery instead of the smaller and lighter 25 amp battery.
    Things sure has changed for the better.
     
    Last edited: Apr 10, 2019
  16. Apr 11, 2019 #16

    bifft

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    A SD-8 and small lithium battery is all I have in my RV. Seems to run the transponder, com and (so far) ADS-b out just fine. Minimal day-VFR panel and no lights.
     
  17. Apr 11, 2019 #17

    cluttonfred

    cluttonfred

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    Thanks, all, for the feedback, not the answer I wanted but not unreasonable either.
     
  18. Apr 11, 2019 #18

    Toobuilder

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    While that may work, from a regulatory standpoint the argument could easily be made that it violates acceptable engineering practice/ guidance. One does need some "reserve", and on paper your transponder alone consumes all of the SD-8's output. The remaining slack is taken up by the battery. Ergo, you do not have an "engine driven electrical system". That would be my argument to the Feds anyway.
     
  19. Apr 11, 2019 #19

    Pops

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    If you bought a new Ercoupe in 1946/47 with the 15 amp charging system and also bought the add-on position lights, landing lights (2) and RB , not counting a tube radio, with everything on at one time you were using more than the system could produce and violating acceptable engineering practice in today's world. They installed a 35 amp battery to last a little longer before the battery went dead over a 25 amp battery. Must had been OK with the CAA at the time.
     
  20. Apr 11, 2019 #20

    Marc Zeitlin

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    Yes, one should plan on running an alternator at 80% or less of it's maximum rated capacity, which for the SD-8 would be 6A.

    But I don't know why you keep insisting that transponders will suck up all the current output. For example, the Stratus ESG (ADS-B out compliant as well, for that matter) states a power requirement of 15W, or just barely over 1A. This would be 15% - 20% of the SD-8's capability. The Garmin GTR-225 COM radio has a typical (non-transmitting) current draw of 0.6A - barely 10% of the SD-8's output.

    So if one has ancient radios/transponders, yes - the SD-8 may not be sufficient. But for modern avionics, it's more than adequate for a simple day VFR aircraft, and would clearly qualify as an "engine driven electrical system".
     
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